Nerves and Action potentials Flashcards
CNS glial (non neuronal) cells
- astrocytes
–> secrete neurotrophic factors, regulate extracellular environment, neurotransmitter uptake and help form blood-brain barrier, source of neural stem cells, provides substrates for ATP production - oligodendrocytes
–> provides the myelin in the CNS - microglial cells
–> immune, uses phagocytosis as defence mechanism - ependymal cells
–> create barriers for compartmentalisation, source of neural stem cells
neurotrophic factors
- it is responsible for guiding neurons, specifically their axons, to the correct target
- promote the survival of neurons during development and throughout the lifespan
- regeneration and sprouting of axons after damage.
*
PNS glial (non neuronal) cells
schwann cells
–>produce myelin
satellite cells
–> support cell bodies
Structure and function of the anatomy of a Neuron
Dendrites: receive input signals or stimuli from other neurons or sensory cells.
Cell Body (Soma): contains the nucleus and other cellular organelles –> integrates the incoming signals received from dendrites and makes a decision on whether to generate an action potential.
Axon Hillock: a specialized region of the cell body.
–> It plays a critical role in determining whether an action potential is generated in the neuron. determines to check If the integrated signals does reach the threshold, for action potential to be initiated.
Axon: It transmits the signal along its length toward the synaptic terminals. Signal Transmission is Unidirectional Flow: starts at the dendrites, passes through the cell body, and travels along the axon to the synaptic terminals.
Synaptic Terminals: form synapses where axon terminal communicates with postsynpatic target cells ; neurotransmitters are released to transmit the signal to the next cell.
Describe the interrelationship of electrical, chemical and electrochemical gradients.
An electrochemical gradient is a combined force resulting from both the electrical gradient (voltage difference) and the chemical gradient (concentration difference) across a cell membrane.
Demonstrate an understanding of membrane potential and how it is generated.
At rest, the intracellular compartment (IC) is high in K+, and the extracellular compartment (EC) is high in Na+.
the IC compartment has a negative charge relative
to the EC compartment (-70mV; resting potential)
The membrane potential is affected by altering
membrane permeability to certain ions
If K + permeability increases, potential = more negative [K+ will flow out]
If Na+ permeability increases, potential = more positive [Na+ will flow in]
Describe the generation of a graded potential
- any stimulus that can open gated ion channels in the cell membrane e.g. mechanical, chemical, or electrical.
- occur locally and are confined to the specific region of the cell membrane where the stimulus is applied.
- they do not propagate over long distances.
Graded potentials can be either depolarizations or hyperpolarizations:
Depolarization: an increase in positive charge inside the cell, (e.g., entry of Na+).
Hyperpolarization: a more negative charge inside the cell, (e.g., exit of K+).
Repolarization: return of the membrane potential to its resting state after a graded potential.
–> They are crucial for influencing the generation of action potentials in neurons.
Describe generation of an action potential
Action Potentials: when a graded potential reaches the axon hillock and depolarizes the membrane to a threshold level.
must be above ‘threshold’ in the trigger zone [needs to last longer to the site where it would be initiated, see if it is still above threshold = action potential]
capable of propagating over long distances along the axon.
Action potentials follow an all-or-none principle
Phases:
* Depolarization Phase
* Repolarization Phase
* Hyperpolarization (Afterpotential) Phas
key differences between the action and graded potential.
Propagation:
Graded potentials do not propagate over long distances and are confined to the site of stimulation/ action potential are capable of propagating over long distances along the axon.
All-or-None vs. Graded Responses:
Action potentials follow an all-or-none response, where reaching the threshold triggers a full action potential.
Graded potentials exhibit a graded response, with the magnitude of the response proportional to the strength of the stimulus.
Location:
Graded potentials occur at dendrites and cell bodies.
Action potentials are typically initiated at the axon hillock.
Graded potentials do not regenerate. This means that as the graded potential travels away from the site of the stimulus, its strength diminishes or decreases. The electrical signal weakens as it travels through the cell membrane, and its effects diminish over distance.
Action potentials have the ability to regenerate. This means that as the action potential travels along the axon, it maintains its strength and does not diminish due to the presence of voltage-gated ion channels along the axon. These channels open in response to the depolarization of the membrane, allowing the influx of ions and the propagation of the action potential. This process repeats along the length of the axon
Understand the concept of summation
The concept of summation in neuroscience refers to the combining of multiple graded potentials to reach the threshold for generating an action potential. There are two main types of summation: temporal summation and spatial summation.
describe the differences between temporal and spatial summation.
Temporal Summation: when two or more graded potentials arrive at the same location on the neuron’s membrane in rapid succession.
Same Location, Close in Timing:
The key characteristic of temporal summation is that the graded potentials are generated at the same synaptic input location, but they occur closely in time.
–> Each individual signal may be sub-threshold, but the cumulative effect of the signals, when combined in time, may lead to the generation of an action potential.
Spatial Summation: when two or more graded potentials, each generated at different synaptic input locations on the neuron’s membrane, arrive simultaneously.
Close in Location, Same Timing:
–> if the individual graded potentials are sub-threshold, their effects can add up spatially=an action potential will be generated.
Diff:
Temporal Summation: Graded potentials combine over time at the same synaptic input location.
Spatial Summation: Graded potentials combine simultaneously but at different synaptic input locations.
threshold def
Threshold is a depolarisation large enough to trigger
opening of voltage-gated Na + channels (~-60 to -55mV)
depolarisation def
a change in the membrane potential of a cell where the inside of the cell becomes less negative compared to the resting membrane potential.
= an influx of positive ions, typically sodium ions (Na+), making the membrane potential less negative or more positive.
repolarisation def
the process of restoring the membrane potential of a cell back to its resting state after depolarization or hyperpolarization [action potentials –> repolarization follows the depolarization phase]
= the efflux of ions that were responsible for depolarization, typically potassium ions (K+), allowing the cell to return to its resting membrane potential.
hyperpolarisation def
a change in the membrane potential of a cell, leading to an increase in the negativity of the inside of the cell compared to the resting membrane potential.
= an efflux of positive ions, often potassium ions (K+), or an influx of negative ions, such as chloride ions (Cl-).
